Planarized interlayer dielectric with air gap isolation

ABSTRACT

A semiconductor device includes an interlayer insulating layer including a first insulating layer on a substrate, and a plurality of interconnections in the first insulating layer. The interlayer insulating layer includes a first region, and a second region including an air gap. The air gap is defined between a pair of the interconnections in the second region. A top surface of the first insulating layer of the first region is lower than a top surface of at least one of the interconnections in the first region.

CROSS-REFERENCE TO RELATED APPLICATIONS

This U.S. non-provisional patent application claims priority under 35U.S.C. § 119 to Korean Patent Application No. 10-2015-0178376, filed onDec. 14, 2015, in the Korean Intellectual Property Office, thedisclosure of which is hereby incorporated by reference in its entirety.

FIELD

The present disclosure relates a semiconductor device and method formanufacturing the same. More specifically, the present disclosurerelates planarizing a dielectric height in a semiconductor processhaving air gaps.

BACKGROUND

Semiconductor devices are widely used in the electronics industrybecause of their small sizes, multi-functional characteristics, and lowmanufacture costs. Several common categories of semiconductor devicesinclude semiconductor memory devices to store logic data, semiconductorlogic devices processing operations of the logic data, and hybridsemiconductor devices, which perform a variety of functions.

Highly integrated semiconductor devices have been increasingly demandedas the electronic industry continues to provide more functions andgreater performance on a single device. Increased levels of integrationmay give rise to various manufacturing problems, for example a marginreduction of an exposure process defining fine patterns. Manufacture ofsemiconductor devices may become difficult due to these problems. Inaddition, high-speed semiconductor devices have been increasinglydemanded with the development of the electronic industry. Variousresearch has been conducted for new techniques capable of realizing highfunctional integration, high-speed or both in semiconductor devices.

Various packaging techniques have been developed to meet the electronicindustry's demand for higher functional capacity, thinner and smallersemiconductor devices, including similar goals for the electronicproducts that include theses devices. In one package technique, varioussemiconductor devices (“chips”) may be vertically stacked to realize ahigh-dense chip stack structure. According to this technique,semiconductor chips having various functions may be integrated on asmaller area than in a general package having one semiconductor chip.

SUMMARY

Embodiments of the inventive concepts may provide a semiconductor devicecapable of reducing or minimizing a capacitance betweeninterconnections.

Embodiments of the inventive concepts may also provide a method ofmanufacturing a semiconductor device, which is capable of effectivelyreducing or minimizing a capacitance between interconnections through asimple process.

In an aspect, a semiconductor device may include an interlayerinsulating layer including a first insulating layer on a substrate, anda plurality of interconnections in the first insulating layer. Theinterlayer insulating layer may include a first region and a secondregion including an air gap. The air gap may be defined between a pairof the interconnections in the second region, and a top surface of thefirst insulating layer of the first region may be lower than a topsurface of at least one of the interconnections in the first region.

In an aspect, a semiconductor device may include a first interlayerinsulating layer on a substrate, a plurality of first interconnectionsdisposed in the first interlayer insulating layer, and barrier patternsbetween the first interlayer insulating layer and the firstinterconnections. The first interlayer insulating layer may include afirst region and a second region including a first air gap. At least oneof the first interconnections in the second region may include a firstportion adjacent to the first air gap. A top surface of the firstportion may be lower than a top surface of the barrier pattern.

In an aspect, a method of manufacturing a semiconductor device mayinclude forming a plurality of interconnections in a first insulatinglayer on a substrate, the first insulating layer including a firstregion and a second region, forming a mask pattern that covers the firstregion and exposes the second region, etching the first insulating layerof the second region using the mask pattern as an etch mask to form anempty space between a pair of the interconnections in the second region,and forming a second insulating layer on the first insulating layer toform an air gap from the empty space. The mask pattern may be removedduring the etching of the first insulating layer.

In an aspect, a method of manufacturing a semiconductor device comprisesforming on a first insulator disposed on a substrate, a plurality ofgrooves having parallel alignment. The grooves have a first regionwherein the grooves are loosely spaced to each other, and a secondregion wherein the grooves are tightly spaced to each other. A barrieris formed on a respective surface of each of the grooves. The barrier isconfigured to isolate a metallic species from the first insulator. Ametallic conductor comprising the metallic species is formed on therespective barrier of each of the grooves. A mask is formed with anopening exposing the second region. A recessed region in the firstinsulator between each of the metallic conductors is formed with a firstetch. The mask and the first insulator between each of the metallicconductors is removed with a second etch. A top surface of each of themetallic conductors is etched with the second etch. A second insulatoris deposited on the first insulator to form an enclosed air gap betweeneach metallic conductor.

BRIEF DESCRIPTION OF THE DRAWINGS

The inventive concepts will become more apparent in view of the attacheddrawings and accompanying detailed description.

FIG. 1 is a plan view illustrating an embodiment of a semiconductordevice according to the inventive concepts.

FIG. 2A and FIG. 2B are cross-sectional views taken along lines I-I′ andII-II′ of FIG. 1, respectively.

FIG. 3A and FIG. 3B are enlarged cross-sectional views of an embodimentof regions ‘M’ and ‘N’ of FIG. 2A, respectively.

FIG. 4A and FIG. 4B are enlarged cross-sectional views of anotherembodiment of regions ‘M’ and ‘N’ of FIG. 2A, respectively.

FIG. 5, FIG. 6A and FIG. 6B are a plan view, a cross-sectional viewtaken along lines I-I′ of FIG. 5, and a cross-sectional view taken alongII-IP of FIG. 5 respectively, illustrating the foil cation of anembodiment of a semiconductor device.

FIG. 7, FIG. 8A and FIG. 8B are a plan view, a cross-sectional viewtaken along lines I-I′ of FIG. 7, and a cross-sectional view taken alongII-II′ of FIG. 7 respectively, illustrating the subsequent processing ofthe embodiment of FIG. 5.

FIG. 9, FIG. 10A and FIG. 10B are a plan view, a cross-sectional viewtaken along lines I-I′ of FIG. 9, and a cross-sectional view taken alongII-II′ of FIG. 9 respectively, illustrating the subsequent processing ofthe embodiment of FIG. 7.

FIG. 11, FIG. 12A and FIG. 12B are a plan view, a cross-sectional viewtaken along lines I-I′ of FIG. 11, and a cross-sectional view takenalong II-II′ of FIG. 11 respectively, illustrating the subsequentprocessing of the embodiment of FIG. 9.

FIG. 13, FIG. 14A and FIG. 14B are a plan view, a cross-sectional viewtaken along lines I-I′ of FIG. 13, and a cross-sectional view takenalong II-II′ of FIG. 13 respectively, illustrating the subsequentprocessing of the embodiment of FIG. 11.

FIG. 15, FIG. 16A and FIG. 16B are a plan view, a cross-sectional viewtaken along lines I-I′ of FIG. 15, and a cross-sectional view takenalong II-II′ of FIG. 15 respectively, illustrating the subsequentprocessing of the embodiment of FIG. 13.

FIG. 17, FIG. 18A and FIG. 18B are a plan view, a cross-sectional viewtaken along lines I-I′ of FIG. 17, and a cross-sectional view takenalong II-II′ of FIG. 17 respectively, illustrating the subsequentprocessing of the embodiment of FIG. 15.

FIG. 19, FIG. 20A and FIG. 20B are a plan view, a cross-sectional viewtaken along lines I-I′ of FIG. 19, and a cross-sectional view takenalong II-II′ of FIG. 19 respectively, illustrating the subsequentprocessing of the embodiment of FIG. 17.

FIG. 21, FIG. 22A and FIG. 22B are a plan view, a cross-sectional viewtaken along lines I-I′ of FIG. 21, and a cross-sectional view takenalong II-II′ of FIG. 21 respectively, illustrating the subsequentprocessing of the embodiment of FIG. 19.

FIG. 23 is a cross-sectional view taken along line I-I′ of FIG. 15 toillustrate a step in the manufacturing of a semiconductor device,according to a comparative example.

FIG. 24 is a plan view illustrating an embodiment of a semiconductordevice according to the inventive concepts.

FIG. 25 is a cross-sectional view taken along a line III-III′ of FIG.24.

FIG. 26 is a plan view illustrating a step in the manufacturing of asemiconductor device, according to some embodiments of the inventiveconcepts.

FIG. 27 is a cross-sectional view taken along a line of FIG. 26.

FIG. 28 is a plan view illustrating an embodiment of a semiconductordevice according to the inventive concepts.

FIG. 29A and FIG. 29B are cross-sectional views taken along lines I-I′and II-II′ of FIG. 28, respectively.

DETAILED DESCRIPTION

Exemplary embodiments of aspects of the present inventive conceptsexplained and illustrated herein include their complementarycounterparts. The same reference numerals or the same referencedesignators denote the same elements throughout the specification.

FIG. 1 is a plan view illustrating an embodiment of a semiconductordevice according to the inventive concepts. FIG. 2A and FIG. 2B arecross-sectional views taken along lines I-I′ and II-II′ of FIG. 1,respectively. FIG. 3A and FIG. 3B are enlarged cross-sectional views ofregions ‘M’ and ‘N’ of FIG. 2A, respectively, to illustrate asemiconductor device according to some embodiments of the inventiveconcepts. FIG. 4A and FIG. 4B are enlarged cross-sectional views ofregions ‘M’ and ‘N’ of FIG. 2A, respectively, to illustrate asemiconductor device according to some embodiments of the inventiveconcepts.

Referring to FIG. 1, FIG. 2A, FIG. 2B, FIG. 3A, and FIG. 3B, anintegrated circuit (IC) may be disposed on a substrate 100. For example,the substrate 100 may be a silicon substrate, a germanium substrate, ora silicon-germanium substrate. In some embodiments, the IC may includeone or more of logic cells for processing data, a control circuit, and apower source circuit for controlling operations of the logic cells. Incertain embodiments, the IC may include one ore more of memory cells forstoring data, a control circuit, and a power source circuit forcontrolling operations of the memory cells.

The IC may include a plurality of transistors TR. The transistors TR mayconstitute the logic cells or the memory cells. Each of the transistorsTR may include a gate electrode GE, a gate dielectric layer GI disposedbetween the gate electrode GE and the substrate 100, a capping patternCP covering a top surface of the gate electrode GE, and dopant regionsDR disposed at both sides of the gate electrode GE. The dopant regionsDR may correspond to portions of the substrate 100, which are doped withdopants. In some embodiments, the gate electrode GE may have a linearshape extending in a first direction D1 parallel to a top surface of thesubstrate 100. Device isolation layers ST formed in the substrate 100may be adjacent to the transistors TR. In one embodiment, the isolationlayer is a shallow trench isolation.

A first interlayer insulating layer ID1 and a second interlayerinsulating layer ID2 may be sequentially stacked on the substrate 100.The first interlayer insulating layer ID1 may include a first insulatinglayer 110 covering the transistors TR, and a second insulating layer 120disposed on the first insulating layer 110. The second insulating layer120 may cover top surfaces of lower interconnections M11 and M12 to bedescribed below. The second interlayer insulating layer ID2 may includea third insulating layer 130 covering the second insulating layer 120,and a fourth insulating layer 140 disposed on the third insulating layer130. The fourth insulating layer 140 may cover top surfaces of upperinterconnections M21 and M22 to be described below. In some embodiments,each of the first and third insulating layers 110 and 130 may include aSilicon Oxide layer, and each of the second and fourth insulating layers120 and 140 may include a Silicon Nitride layer or a SiliconCarbonitride (SiCN) layer.

The first interlayer insulating layer ID1 may include a first region RG1and a second region RG2. The second region RG2 may be a region in whichfirst air gaps AG1 to be described below are disposed. The second regionRG2 corresponds to an area in which metal interconnects extending in thesecond direction D2 are tightly spaced to each other relative to thephotolithographic limitations used to fabricate the IC. The secondinterlayer insulating layer ID2 may include a third region RG3 and afourth region RG4. The fourth region RG4 may be a region in which secondair gaps AG2 to be described below are disposed. The fourth region RG4corresponds to an area in which metal interconnects extending in thefirst direction D1 are tightly spaced to each other relative to thephotolithographic limitations used to fabricate the IC.

A plurality of lower interconnections M11 and M12 may be disposed in thefirst insulating layer 110. The lower interconnections M11 and M12 mayhave linear shapes extending in a second direction D2 intersecting thefirst direction D1. At least one of the lower interconnections M11 andM12 may have a vertical extension VP (e.g., a contact or a via)extending toward the substrate 100. In some embodiments, at least one ofthe lower interconnections M11 and M12 may be electrically connected tothe dopant region DR through the vertical extension VP. In certainembodiments, at least one of the lower interconnections M11 and M12 maybe electrically connected to the gate electrode GE through the verticalextension VP. The lower interconnections M11 and M12 may include a metalsuch as Copper (Cu) or Tungsten (W).

Barrier patterns BP may be disposed between the first insulating layer110 and the lower interconnections M11 and M12, respectively. Each ofthe barrier patterns BP may directly cover a bottom surface and bothsidewalls of each of the lower interconnections M11 and M12. The barrierpatterns BP may prevent a metal material from being diffused from thelower interconnections M11 and M12 into the first interlayer insulatinglayer ID1. For example, the barrier patterns BP may include Titanium(Ti), Titanium Nitride (TiN), or a combination thereof.

The lower interconnections M11 and M12 may include first lowerinterconnections M11 disposed in the first region RG1 and second lowerinterconnections M12 disposed in the second region RG2. A patterndensity of the first lower interconnections M11 in the first region RG1may be different from a pattern density of the second lowerinterconnections M12 in the second region RG2. In some embodiments, thepattern density of the first lower interconnections M11 in the firstregion RG1 may be lower than the pattern density of the second lowerinterconnections M12 in the second region RG2. In other words, anaverage distance between the first lower interconnections M11 adjacentto each other may be greater than an average distance between the secondlower interconnections M12 adjacent to each other.

First air gaps AG1 surrounded by the second insulating layer 120 may bedefined between the second lower interconnections M12. In other words,each of the first air gaps AG1 may be disposed between a pair of thesecond lower interconnections M12 adjacent to each other. The secondinsulating layer 120 may not completely fill spaces between the secondlower interconnections M12, and thus empty spaces between the secondlower interconnections M12 may be defined as the first air gaps AG1. Insome embodiments, the first air gaps AG1 may have linear shapesextending along the second lower interconnections M12 in the seconddirection D2 when viewed from a plan view. However, embodiments of theinventive concepts are not limited thereto. In one embodiment, the firstair gaps AG1 are formed due to the lack of conformal coating of thesecond insulating layer 120 due to the relatively narrow spacing of thesecond lower interconnections M12. In another embodiment, the first airgaps AG1 are fruited by a combination of dry (e.g. plasma) andHydrofluoric (HF) wet etching processes. Narrowly spacedinterconnections may occur in dense circuit topologies, such as inmemory cell arrays or programmable gate arrays.

Because the pattern density of the second lower interconnections M12 isrelatively high, a parasitic capacitance between the second lowerinterconnections M12 may be increased. Thus, RC delay of a semiconductordevice may be increased. However, the first air gaps AG1 may reducedielectric constants between the second lower interconnections M12. As aresult, an operating speed of the semiconductor device may be improved.The air gaps AG1 will also reduce parasitic coupling between adjacentinterconnections (e.g., between adjacent bit lines in a memory array).

A top surface of the first insulating layer 110 of the first region RG1may be higher than a top surface of the first insulating layer 110 ofthe second region RG2. Conversely, a top surface of the secondinsulating layer 120 of the first region RG1 may be substantiallycoplanar with a top surface of the second insulating layer 120 of thesecond region RG2. In one example, the first insulating layer 110 isconformally deposited, while the second insulating layer 120 isplanarized after being deposited.

A plurality of upper interconnections M21 and M22 may be disposed in thethird insulating layer 130. The upper interconnections M21 and M22 mayhave linear shapes extending in the first direction D1. At least one ofthe upper interconnections M21 and M22 may have a vertical extension VPextending toward the substrate 100. In some embodiments, at least one ofthe upper interconnections M21 and M22 may be electrically connected toat least one of the lower interconnections M11 and M12 through thevertical extension VP thereof. The upper interconnections M21 and M22may include a metal such as Copper (Cu) or Tungsten (W). Barrierpatterns BP may be disposed between the third insulating layer 130 andthe upper interconnections M21 and M22, respectively. The barrierpatterns BP between the third insulating layer 130 and the upperinterconnections M21 and M22 may have the same or similar function asthe barrier patterns BP between the first insulating layer 110 and thelower interconnections M11 and M12.

The upper interconnections M21 and M22 may include first upperinterconnections M21 disposed in the third region RG3 and second upperinterconnections M22 disposed in the fourth region RG4. A patterndensity of the first upper interconnections M21 in the third region RG3may be lower than a pattern density of the second upper interconnectionsM22 in the fourth region RG4.

Second air gaps AG2 surrounded by the fourth insulating layer 140 may bedefined between the second upper interconnections M22. The fourthinsulating layer 140 may not completely fill spaces between the secondupper interconnections M22, and thus empty spaces between the secondupper interconnections M22 may be defined as the second air gaps AG2. Insome embodiments, the second air gaps AG2 may have linear shapesextending along the second upper interconnections M22 in the firstdirection D1 when viewed from a plan view. However, embodiments of theinventive concepts are not limited thereto. Dielectric constants betweenthe second upper interconnections M22 may be reduced by the second airgaps AG2.

A top surface of the third insulating layer 130 of the third region RG3may be higher than a top surface of the third insulating layer 130 ofthe fourth region RG4. Conversely, a top surface of the fourthinsulating layer 140 of the third region RG3 may be substantiallycoplanar with a top surface of the fourth insulating layer 140 of thefourth region RG4. In one example, the third insulating layer 130 isconformally deposited, while the fourth insulating layer 140 isplanarized after being deposited. In other embodiments, additionalinterlayer insulating layers and additional interconnections may bestacked on the second interlayer insulating layer ID2. However,embodiments of the inventive concepts are not limited thereto.

Referring again to FIG. 3A and FIG. 3B, each of the second upperinterconnections M22 may have a first recess RS1 on an edge thereof. Thefirst recess RS1 may be adjacent to the second air gap AG2. Thus, eachof some of the second upper interconnections M22 may have one firstrecess RS1. The second upper interconnection M22 disposed between thesecond air gaps AG2 may also have a pair of the first recesses RS1respectively formed on both edges thereof.

Specifically, the second upper interconnection M22 disposed between thesecond air gaps AG2 may include a pair of first portions P1 respectivelyadjacent to the second air gaps AG2 and a second portion P2corresponding to a central portion thereof. The second portion P2 may bedisposed between the pair of first portions P1. The pair of firstrecesses RS1 may exist on each of the pair of first portions P1,respectively. Top surfaces P1 t of the first portions P1 may be lowerthan a top surface BPt of the barrier pattern BP. Here, the top surfaceBPt of the barrier pattern BP may be a top end of the barrier patternBP. A top surface P2 t of the second portion P2 may be disposed atsubstantially the same level as, or a lower level than, the top surfaceBPt of the barrier pattern BP. The first recesses RS1 may prevent metalatoms of the second upper interconnections M22 from moving toneighboring upper interconnections over the barrier patterns BP.

One or more of the second upper interconnections M22 may have one firstportion P1 wherein the top surface P1 t is lower than the top surfaceBPt of the barrier pattern BP. In contrast the top surfaces M21 t of thefirst upper interconnections M21, (in the third region RG3), may besubstantially coplanar with the top surface BPt of the barrier patternBP. A top surface 130 t of the third insulating layer 130 of the thirdregion RG3 may be lower than the top surface M21 t of the first upperinterconnection M21.

A width of each of the second air gaps AG2 may gradually decrease as avertical distance from the top surface of the substrate 100 (i.e., aheight in a third direction D3) increases. In other words, each of thesecond air gaps AG2 may have an arrowhead shape with a point at the topas shown in FIG. 3A, or a pentagon with a wider base. A top of thesecond air gap AG2 may be higher than the top surface (e.g. P2 t) of thesecond upper interconnection M22.

A thickness of the fourth insulating layer 140 surrounding the secondair gap AG2 may vary. In some embodiments, the fourth insulating layer140 under the second air gap AG2 may have a first thickness T1. Thefourth insulating layer 140 at a side of the second air gap AG2 may havea second thickness T2. The minimum thickness of the fourth insulatinglayer 140 on top of the second air gap AG2 may be a third thickness T3.Here, the first thickness T1 may be greater than the second thicknessT2, and the third thickness T3 may be greater than the first thicknessT1.

FIG. 4A and FIG. 4B illustrate an embodiment of upper interconnectionsdifferent from that shown in FIG. 3A and FIG. 3B, respectively. Forclarity of explanation, the descriptions of the same technical featuresas in the embodiment of FIG. 3A and FIG. 3B will be omitted, ormentioned briefly, rather the differences between the embodiments willbe described. Each of the first upper interconnections M21 may have asecond recess RS2 formed on the edge opposing the first recess RS1. Thepair of recesses formed by RS1 and RS2 may be recessed downward from thetop surface BPt of the barrier pattern BP.

At least one of the second upper interconnections M22 may have a firstrecess RS1 formed on one edge adjacent to the second air gap AG2 and asecond recess RS2 formed on another edge, as shown in FIG. 4A. Here, thefirst recess RS1 may be deeper than the second recess RS2. In otherwords, a bottom end of the first recess RS1 may be lower than a bottomend of the first recess RS2. However, the second upper interconnectionM22 disposed between the second air gaps AG2 may have a pair of thefirst recesses RS1 respectively forming on both edges thereof. In otherwords, the second recess RS2 may not exist on the second upperinterconnection M22 disposed between the second air gaps AG2. The firstrecesses RS1 and the second recesses RS2 may prevent metal atoms of theupper interconnections M21 and M22 from moving to neighboring upperinterconnections over the barrier patterns BP.

In the above embodiments, the upper interconnections M21 and M22 and thesecond air gaps AG2 are primarily described with reference to FIG. 3A,FIG. 3B, FIG. 4A, and FIG. 4B. The lower interconnections M11 and M12and their corresponding first air gaps AG1 may be described similarly tothe descriptions provided for FIG. 3A, FIG. 3B, FIG. 4A, and FIG. 4B,and thus the descriptions thereto will be omitted for brevity.

FIGS. 5, 7, 9, 11, 13, 15, 17, 19, and 21 are plan views illustratingprogressive views of an embodiment of a semiconductor device beingmanufactured according to the inventive concepts described herein. FIGS.6A, 8A, 10A, 12A, 14A, 16A, 18A, 20A, and 22A are cross-sectional viewstaken along lines I-I′ of FIGS. 5, 7, 9, 11, 13, 15, 17, 19, and 21,respectively. FIGS. 6B, 8B, 10B, 12B, 14B, 16B, 18B, 20B, and 22B arecross-sectional views taken along lines II-II′ of FIGS. 5, 7, 9, 11, 13,15, 17, 19, and 21, respectively.

Referring to FIG. 5, FIG. 6A, and FIG. 6B, an IC may be formed on asubstrate 100. For example, the substrate 100 may be a siliconsubstrate, a germanium substrate, or a silicon-germanium substrate.

Forming the IC may include forming a plurality of transistors TR. Insome embodiments, device isolation layers ST (e.g. shallow trenchisolation) may be formed in the substrate 100 to define active regions.A gate dielectric layer GI, a gate electrode GE, and a capping patternCP may be formed on the active region. The gate electrode GE mayintersect the active region, and the gate dielectric layer GI may bedisposed between the gate electrode GE and the substrate 100. Thecapping pattern CP may cover a top surface of the gate electrode GE.Dopant regions DR may be formed at both sides of the gate electrode GE.The dopant regions DR may be formed by doping portions of the activeregion (e.g., the substrate 100), which are disposed at both sides ofthe gate electrode GE, with dopants. Subsequently, a first insulatinglayer 110 covering the transistors TR may be formed on an entire topsurface of the substrate 100. The first insulating layer 110 may includea first region RG1 and a second region RG2. For example, the firstinsulating layer 110 may include a Silicon Oxide layer.

The first insulating layer 110 may be patterned to form lowerinterconnection grooves H11 and H12 extending in a second direction D2.The lower interconnection grooves H11 and H12 may be formed in an upperportion of the first insulating layer 110, and thus bottom surfaces ofthe lower interconnection grooves H11 and H12 may be higher than abottom surface of the first insulating layer 110. In some embodiments,at least one of the lower interconnection grooves H11 and H12 mayinclude a vertical extension hole VPH extending toward the substrate100. In some embodiments, the vertical extension hole VPH may penetratethe first insulating layer 110 to expose a portion of the dopant regionDR. In certain embodiments, the vertical extension hole VPH maypenetrate the first insulating layer 110 and the capping pattern CP toexpose a portion of the gate electrode GE. Thus the vertical extensionhole VPH can be used to form a contact or via connection betweenmetallic interconnect and active terminals of a semiconductortransistor.

The lower interconnection grooves H11 and H12 may include first lowerinterconnection grooves H11 disposed in the first region RG1 and secondlower interconnection grooves H12 disposed in the second region RG2. Insome embodiments, a pattern density of the first lower interconnectiongrooves H11 in the first region RG1 may be lower than a pattern densityof the second lower interconnection grooves H12 in the second regionRG2. In other words, the spacing between the grooves H12 in the secondregion RG2 is smaller than the spacing between the grooves H11 in thefirst region RG1.

Referring to FIG. 7, FIG. 8A, and FIG. 8B, first and second lowerinterconnections M11 and M12 may be formed to fill the first and secondlower interconnection grooves H11 and H12, respectively (e.g., with adual damascene process). In some embodiments, a barrier layer may beformed on the first insulating layer 110 and inner surfaces of the lowerinterconnection grooves H11 and H12. The barrier layer may partiallyfill the lower interconnection grooves H11 and H12. For example, thebarrier layer may include Titanium (Ti), Titanium Nitride (TiN), or acombination thereof. In one embodiment, the barrier layer is depositedwith an Atomic Layer Deposition process and is the same as the barrierpattern BP shown in FIG. 3A to FIG. 4B.

Subsequently, a conductive layer may be formed on the barrier layer. Theconductive layer may completely fill the lower interconnection groovesH11 and H12. The conductive layer may be formed of a metal such asCopper (Cu) and Tungsten (W). In some embodiments, the conductive layermay be formed by a plating process. In this case, a seed layer (notshown) may be formed on the barrier layer. The conductive layer may beformed by the plating process using the seed layer as a seed.

The conductive layer and the barrier layer may be planarized (e.g, withChemical Mechanical Polishing), to form the lower interconnections M11and M12 and barrier patterns BP in the lower interconnection grooves H11and H12, respectively. Thus, top surfaces of the lower interconnectionsM11 and M12 may be substantially coplanar with a top surface of thefirst insulating layer 110, as shown in FIG. 8B.

Referring to FIG. 9, FIG. 10A, and FIG. 10B, a first mask layer ML maybe formed on the first insulating layer 110. The first mask layer ML maydirectly cover the lower interconnections M11 and M12. For example, thefirst mask layer ML may be formed of a Silicon Nitride layer.

Referring to FIG. 11, FIG. 12A, and FIG. 12B, the first mask layer MLmay be patterned to form first mask patterns MP1. The first maskpatterns MP1 may be formed to expose the first insulating layer 110 ofthe second region RG2. In other words, the first mask patterns MP1 mayselectively cover the first region RG1. The first mask patterns MP1 mayhave a first opening OP1 exposing the second region RG2.

The first mask layer ML may be patterned using a dry etching process. Aportion of the first mask layer ML, which is disposed on the secondregion RG2, may be removed using the dry etching process. After theportion of the first mask layer ML disposed on the second region RG2 isremoved, over-etching may be performed. Thus, an upper portion of thefirst insulating layer 110 of the second region RG2 may be recessed byover-etching to form first shallow recess regions 112. The first shallowrecess regions 112 may be formed between the second lowerinterconnections M12.

Conversely, upper portions of the second lower interconnections M12exposed through the first opening OP1 may be recessed by theover-etching step. Thus, first recesses RS1 may be formed on edges ofthe second lower interconnections M12, (see FIG. 3A). If theaforementioned planarization of the conductive layer and the barrierlayer is incompletely performed, a portion of the conductive layer mayremain between the second lower interconnections M12, causing anelectrical short. However, the second lower interconnections M12 may becompletely insulated from each other by over-etching.

Referring to FIG. 13, FIG. 14A, and FIG. 14B, the first insulating layer110 of the second region RG2 may be etched using the first mask patternsMP1 as etch masks to form first empty spaces 114 between the secondlower interconnections M12. In some embodiments, etching the firstinsulating layer 110 may be performed by a wet etching process usingHydrofluoric (HF) acid. The first empty spaces 114 may extend along thesecond lower interconnections M12 in the second direction D2. The firstempty spaces 114 may expose sidewalls of the barrier patterns BP. Inother embodiments, other isotropic etch methods are used to etch thefirst shallow recess regions 112 to form the empty spaces 114.

In addition, the first mask patterns MP1 may be completely removedduring the wet etching process. Subsequently, an upper portion of thefirst insulating layer 110 of the first region RG1 may be exposed andthen may be recessed by over-etching. Thus, a top surface of the firstinsulating layer 110 of the first region RG1 may be lower than topsurfaces of the first lower interconnections M11, (see FIG. 3B).

In addition, the exposed lower interconnections M11 and M12 may beslightly recessed during the wet etching process, thereby forming secondrecesses RS2 on edges of the lower interconnections M11 and M12 (SeeFIG. 4A and FIG. 4B). Like the first recesses RS1 described above, thelower interconnections M11 and M12 may be completely insulated from eachother by the second recesses RS2, shown in FIG. 4A and FIG. 4B.

Referring to FIG. 15, FIG. 16A, and FIG. 16B, a second insulating layer120 may be formed on the first insulating layer 110 and the lowerinterconnections M11 and M12. The first and second insulating layers 110and 120 may constitute a first interlayer insulating layer ID1. Forexample, the second insulating layer 120 may be formed of a SiliconNitride layer or a Silicon Carbonitride (SiCN) layer.

The second insulating layer 120 may be formed using a deposition processhaving poor step coverage, (e.g., a Chemical Vapor Deposition (CVD)process or a Physical Vapor Deposition (PVD) process). The secondinsulating layer 120 may partially fill the first empty spaces 114during the deposition process. Here, the first empty spaces 114 may becapped by the second insulating layer 120 deposited on the second lowerinterconnections M12 before the second insulating layer 120 completelyfills the first empty spaces 114. Thus, first air gaps AG1 surrounded bythe second insulating layer 120 may be formed from the first emptyspaces 114. A thickness of the second insulating layer 120 surroundingthe first air gap AG2 may vary according to a position by the depositionprocess having the poor step coverage property, (see FIG. 3A).

FIG. 23 is a cross-sectional view corresponding taken along line I-I′ ofFIG. 15 to illustrate a method of manufacturing a semiconductor device,according to a comparative example. Referring to FIG. 23, in someembodiments, the first mask patterns MP1 may remain after the wetetching process described with reference to FIG. 13, FIG. 14A, and FIG.14B. In this case, the first mask patterns MP1 may include SiliconCarbonitride (SiCN). Next, the second insulating layer 120 describedwith reference to FIG. 15, FIG. 16A, and FIG. 16B may be formed to formthe first air gaps AG1, by capping the empty spaces 114 with the secondinsulating layer 120.

Due to the first mask patterns MP1, a height difference may occurbetween the second insulating layer 120 of the first region RG1 and thesecond insulating layer 120 of the second region RG2. The heightdifference may cause defects during formation of upper interconnectionsM21 and M22 and a second interlayer insulating layer ID2 to be describedbelow. Thus in one embodiment, an additional etching process forselectively removing the first mask patterns MP1 should be performedbefore the formation of the second insulating layer 120. In anotherembodiment, a planarization process is performed on the secondinsulating layer 120 after the formation of the second insulating layer120. As a result, this may reduce efficiency (e.g. cost) of processes ofmanufacturing a semiconductor device, as well as increase theprobability of introducing defects in the process by adding additionalsteps.

However, according to some embodiments of the inventive concepts, a topsurface of the second insulating layer 120 of the first region RG1 maybe substantially coplanar with a top surface of the second insulatinglayer 120 of the second region RG2, as illustrated in FIG. 15, FIG. 16A,and FIG. 16B. Thus, embodiments of the inventive concepts that includeremoval of the mask MP1 (see FIG. 13) do not require an additionalprocess. Accordingly, the efficiency of processes of manufacturing thesemiconductor device may be improved.

Referring to FIG. 17, FIG. 18A, and FIG. 18B, a third insulating layer130 may be fruited on the second insulating layer 120. The thirdinsulating layer 130 may include a third region RG3 and a fourth regionRG4. For example, the third insulating layer 130 may include a SiliconOxide layer.

Upper interconnections M21 and M22 extending in the first direction D1intersecting the second direction D2 may be formed in the thirdinsulating layer 130. The upper interconnections M21 and M22 may includefirst upper interconnections M21 formed in the third region RG3 andsecond upper interconnections M22 Ruined in the fourth region RG4. Amethod of forming the upper interconnections M21 and M22 may be the sameor similar as the method of forming the lower interconnections M11 andM12 described with reference to FIG. 5, FIG. 6A, FIG. 6B, FIG. 7, FIG.8A, and FIG. 8B.

Referring to FIG. 19, FIG. 20A, and FIG. 20B, second mask patterns MP2may be formed on the third insulating layer 130. The second maskpatterns MP2 may be formed to expose the third insulating layer 130 ofthe fourth region RG4. Specifically, the second mask patterns MP2 mayselectively cover the third region RG3. The second mask patterns MP2 mayhave a second opening OP2 exposing the fourth region RG4. Forming thesecond mask patterns MP2 may include forming a second mask layer on thethird insulating layer 130 and patterning the second mask layer.

The second mask patterns MP2 may be formed by the same or similar methodas described above with reference to FIG. 11, FIG. 12A, and FIG. 12B.Thus, an upper portion of the third insulating layer 130 of the fourthregion RG4 may be recessed to form second shallow recess regions 132.The second shallow recess regions 132 may be formed between the secondupper interconnections M22.

Upper portions of the second upper interconnections M22 exposed throughthe second opening OP2 may be recessed by over-etching. Thus, firstrecesses RS1 may be formed on edges of the second upper interconnectionsM22, (see FIG. 3A).

Referring to FIG. 21, FIG. 22A, and FIG. 22B, the third insulating layer130 of the fourth region RG4 may be etched using the second maskpatterns MP2 as etch masks to form second empty spaces 134 between thesecond upper interconnections M22. The second empty spaces 134 mayextend along the second upper interconnections M22 in the firstdirection D1.

The etching process of forming the second empty spaces 134 may be thesame or similar as described with reference to FIG. 13, FIG. 14A, andFIG. 14B. Thus, the second mask patterns MP2 may be completely removedduring the etching process. In addition, an upper portion of the thirdinsulating layer 130 of the third region RG3 may be recessed byover-etching. Thus, a top surface 130 t of the third insulating layer130 of the third region RG3 may be lower than top surfaces M21 t of thefirst upper interconnections M21, (see FIG. 3B).

Furthermore, exposed upper interconnections M21 and M22 may be slightlyrecessed during the etching process, thereby forming second recesses RS2on edges of the upper interconnections M21 and M22, (see FIG. 4A andFIG. 4B).

Referring again to FIG. 1, FIG. 2A, and FIG. 2B, a fourth insulatinglayer 140 may be formed on the third insulating layer 130 and the upperinterconnections M21 and M22. The third and fourth insulating layers 130and 140 respectively may constitute a second interlayer insulating layerID2. For example, the fourth insulating layer 140 may be formed of aSilicon Nitride layer or a Silicon Carbonitride (SiCN) layer.

Similar to the second insulating layer 120 described with reference toFIG. 15, FIG. 16A, and FIG. 16B, the fourth insulating layer 140 may beformed using a deposition process having poor step coverage. Thus,second air gaps AG2 surrounded by the fourth insulating layer 140 may beformed from the second empty spaces 134. A thickness of the fourthinsulating layer 140 surrounding the second air gap AG2 may be variedaccording to a position by the deposition process having the poor stepcoverage property, (see FIG. 3A). Conversely, a top surface of thefourth insulating layer 140 of the third region RG3 may be substantiallycoplanar with a top surface of the fourth insulating layer 140 of thefourth region RG4.

FIG. 24 is a plan view illustrating an embodiment of a semiconductordevice according to the inventive concepts. FIG. 25 is a cross-sectionalview taken along a line of FIG. 24. A cross-sectional view taken along aline I-I′ of FIG. 24 may be the same as shown in FIG. 2A, and across-sectional view taken along a line II-II′ of FIG. 24 may be thesame as shown in FIG. 2B. In the present embodiment, the descriptions ofthe same technical features as in the embodiments of FIG. 1, FIG. 2A,FIG. 2B, FIG. 3A, and FIG. 3B will be omitted or mentioned briefly forbrevity and clarity of explanation. Instead, differences between thepresent embodiment and the embodiments of FIG. 1, FIG. 2A, FIG. 2B, FIG.3A, and FIG. 3B will be described.

Referring to FIG. 24, FIG. 25, FIG. 2A, and FIG. 2B, a plurality ofsecond air gaps AG2 may be provided between a pair of second upperinterconnections M22 adjacent to each other. Specifically, the secondair gaps AG2 may be spaced apart from each other and may be arranged ina first direction D1, unlike the second air gap AG2 having the linearshape described with reference to FIG. 1, FIG. 2A, and FIG. 2B. A thirdinsulating layer 130 may include protruding portions 130U disposedbetween the pair of second upper interconnections M22. Each of theprotruding portions 130U may be disposed between the second air gaps AG2adjacent to each other in the first direction D1. Structural stabilityof the second air gaps AG2 may be improved by the protruding portions130U and a fourth insulating layer 140, which fill spaces between thesecond air gaps AG2 and the protruding portions 130U.

In the present embodiment, the plurality of second air gaps AG2 disposedbetween the pair of second upper interconnections M22 are described asan example. Similarly, a plurality of first air gaps AG1 may be arrangedbetween a pair of first lower interconnections M11 adjacent to eachother. However, embodiments of the inventive concepts are not limitedthereto.

FIG. 26 is a plan view illustrating a step in the manufacturing of asemiconductor device, according to the inventive concepts. FIG. 27 is across-sectional view taken along line of FIG. 26. A cross-sectional viewtaken along line I-I′ of FIG. 26 may be the same as shown in FIG. 20A,and a cross-sectional view taken along a line II-II′ of FIG. 26 may bethe same as shown in FIG. 20B. In the present embodiment, thedescriptions of the same technical features as in the manufacturingmethod of FIGS. 5 to 22B will be omitted or mentioned briefly forbrevity and clarity of explanation. Instead, differences between thepresent embodiment and the embodiment of FIGS. 5 to 22B will bedescribed.

Referring to FIG. 26, FIG. 27, FIG. 20A, and FIG. 20B, a second maskpattern MP2 may be formed on the structure illustrated in FIG. 17, FIG.18A, and FIG. 18B. The second mask pattern MP2 may be formed to exposeportions of a third insulating layer 130 of a fourth region RG4.Specifically, the second mask pattern MP2 may have a plurality of secondopenings OP2 exposing portions of the fourth region RG4. The secondopenings OP2 may be arranged along a first direction D1 when viewed froma plan view.

Thus, second shallow recess regions 132 may be formed on the thirdinsulating layer 130 exposed by the second openings OP2. The secondshallow recess regions 132 may be arranged along the first direction D1between the second upper interconnections M22.

Referring again to FIG. 24, FIG. 25, FIG. 2A, and FIG. 2B, the thirdinsulating layer 130 may be etched using the second mask pattern MP2 asan etch mask, and then a fourth insulating layer 140 may be formed onthe third insulating layer 130. Concurrently, second air gaps AG2surrounded by the fourth insulating layer 140 may be formed.

FIG. 28 is a plan view illustrating a semiconductor device according tosome embodiments of the inventive concepts. FIG. 29A and FIG. 29B arecross-sectional views taken along lines I-I′ and II-II′ of FIG. 28,respectively. In the present embodiment, the descriptions to the sametechnical features as in the embodiment of FIG. 1, FIG. 2A, FIG. 2B,FIG. 3A, and FIG. 3B will be omitted or mentioned briefly for brevityand clarity of explanation. Instead, differences between the presentembodiment and the embodiment of FIG. 1, FIG. 2A, FIG. 2B, FIG. 3A, andFIG. 3B will be described. For brevity and clarity, the lower and upperinterconnections and air gaps are omitted in FIG. 28. However, the samelower and upper interconnections and air gaps as illustrated in FIG. 1may be applied to the semiconductor device of FIG. 28.

Referring to FIG. 28, FIG. 29A, and FIG. 29B, an embodiment of a logiccell, (configured to process data), is illustrated. Device isolationlayers ST may be provided in a substrate 100 to define active patternsFN. The device isolation layers ST may be formed in an upper portion ofthe substrate 100. For example, the substrate 100 may be a siliconsubstrate, a germanium substrate, or a silicon-on-insulator (SOI)substrate. For example, the device isolation layers ST may include asilicon oxide layer. In one embodiment, the device isolation layers STare Shallow Trench Isolations (STI), wherein the active patterns FN arelaterally disposed between the STI regions.

The active patterns FN may extend in a second direction D2. The activepatterns FN may be arranged in a first direction D1 intersecting thesecond direction D2. In some embodiments, upper portions of the activepatterns FN may include fin portions, respectively. In some embodiments,each of the fin portions may have a fin-shape protruding along the D3axis, parallel to the device isolation layers ST.

Gate electrodes GE may be provided on the active patterns FN and mayextend in the first direction D1. A gate dielectric layer GI may beprovided under each of the gate electrodes GE, and gate spacers GS (notshown) may be provided on both sidewalls of each of the gate electrodesGE. A capping pattern CP may be provided to cover a top surface of eachof the gate electrodes GE.

The gate electrodes GE may include at least one of a doped semiconductormaterial, a metal, or a conductive Metal Nitride. The gate dielectriclayer GI may include at least one of a Silicon Oxide layer, a SiliconOxynitride layer, or a High-K dielectric layer of which a dielectricconstant is higher than that of a Silicon Oxide layer. Each of thecapping pattern GP and the gate spacer GS may include at least one ofSilicon Oxide, Silicon Nitride, or Silicon Oxynitride.

Source and drain regions SD may be provided on or in the active patternsFN at both sides of each of the gate electrodes GE. The fin portionsdisposed under each of the gate electrodes GE may be used as channelregions AF. Each of the channel regions AF may be disposed between thesource and drain regions SD.

In some embodiments, the source and drain regions SD may includeepitaxial patterns formed using a selective epitaxial growth (SEG)process. The source and drain regions SD may include a differentsemiconductor element from the substrate 100. In some embodiments, thesource and drain regions SD may include a semiconductor element of whicha lattice constant is greater or smaller than that of the semiconductorelement of the substrate 100 (e.g., “strained silicon”). Because thesource and drain regions SD include the different semiconductor elementfrom the substrate 100, compressive stress or tensile stress may beprovided to the channel regions AF.

A first interlayer insulating layer ID1 and a second interlayerinsulating layer ID2 may be sequentially stacked on the substrate 100.The lower interconnections M11 and M12 may be disposed in the firstinterlayer insulating layer ID1, and the upper interconnections M21 andM22 may be disposed in the second interlayer insulating layer ID2. Thefirst air gaps AG1 may be provided between the second lowerinterconnections M12, and the second air gaps AG2 may be providedbetween the second upper interconnections M22. The interlayer insulatinglayers ID1 and ID2, the lower and upper interconnections M11, M12, M21,and M22, and the first and second air gaps AG1 and AG2 may be the sameas described above with reference to FIG. 1, FIG. 2A, FIG. 2B, FIG. 3A,and FIG. 3B.

In the semiconductor device according to some embodiments of theinventive concepts, the air gap may be disposed between theinterconnections having the high pattern density. Thus, the parasiticcapacitance between the interconnections may be reduced or minimized. Inaddition, the interconnections may be effectively insulated from eachother, and thus the reliability of the semiconductor device may beimproved. According to some embodiments of the inventive concepts, theheight difference of the interlayer insulating layer may be removedwithout an additional process, and thus the process reliability may beimproved (e.g. by improving step coverage of subsequently formedmetallic interconnects).

While the inventive concepts have been described with reference toexample embodiments, it will be apparent to those skilled in the artthat various changes and modifications may be made without departingfrom the spirits and scopes of the inventive concepts. Therefore, itshould be understood that the above embodiments are not limiting, butillustrative. Thus, the scopes of the inventive concepts are to bedetermined by the broadest permissible interpretation of the followingclaims and their equivalents, and shall not be restricted or limited bythe foregoing description.

What is claimed is:
 1. A semiconductor device comprising: an interlayerinsulating layer including a first insulating layer on a substrate; aplurality of interconnections in the first insulating layer; and aplurality of barrier patterns between the interlayer insulating layerand the interconnections, respectively, wherein each of the barrierpatterns covers a bottom surface and both sidewalls of each of theinterconnections, wherein the interlayer insulating layer includes afirst region, and a second region including an air gap, wherein the airgap is between a pair of the interconnections in the second region,wherein a top surface of the first insulating layer of the first regionis lower than a top surface of at least one of the interconnections inthe first region, wherein each of the pair of interconnections includesa first portion adjacent to the air gap and a second portion in acentral region adjacent to the first portion, wherein a top surface ofthe first portion is lower than a top surface of the barrier pattern onat least one of the sidewalls, wherein a top surface of the secondportion is higher than a top surface of the first portion, and whereinthe top surface of the second portion is level with or lower than thetop surface of the barrier pattern.
 2. The semiconductor device of claim1, wherein the interlayer insulating layer further includes a secondinsulating layer covering the first insulating layer, and wherein a topsurface of the second insulating layer of the first region is coplanarwith a top surface of the second insulating layer of the second region.3. The semiconductor device of claim 2, wherein the air gap issurrounded by the second insulating layer, and wherein a thickness ofthe second insulating layer under the air gap is thicker than athickness of the second insulating layer at a side of the air gap. 4.The semiconductor device of claim 1, wherein a pattern density of theinterconnections of the first region is less than a pattern density ofthe interconnections of the second region.
 5. The semiconductor deviceof claim 1, wherein at least one of the interconnections in the firstregion has a first recess formed on an edge thereof, the edge defined bya top surface of the first portion in contact with one of the sidewalls.6. The semiconductor device of claim 1, wherein at least one of the pairof interconnections has a first recess and a second recess formed onboth edges thereof, respectively, and wherein the second recess isdeeper than the first recess, wherein each of the edges is defined by arespective top surface of the respective first portion in contact with arespective one of the sidewalls.
 7. The semiconductor device of claim 1,wherein a width of the air gap decreases as a vertical distance from atop surface of the substrate increases.
 8. The semiconductor device ofclaim 7, wherein a top of the air gap is higher than a top surfaces ofeach of the pair of interconnections.
 9. The semiconductor device ofclaim 1, wherein the air gap extends parallel to the pair ofinterconnections in one direction.
 10. The semiconductor device of claim1, wherein the pair of interconnections extends in one direction,wherein a plurality of the air gaps is provided, and wherein theplurality of the air gaps are spaced apart from each other and arearranged parallel to the one direction between the pair ofinterconnections.
 11. A semiconductor device comprising: an interlayerinsulating layer on a substrate; a plurality of interconnections in theinterlayer insulating layer; and a plurality of barrier patterns betweenthe interlayer insulating layer and the interconnections, respectively,wherein each of the barrier patterns covers a bottom surface and bothsidewalls of each of the interconnections, wherein the interlayerinsulating layer includes a first region and a second region includingan air gap, wherein the interconnections includes a firstinterconnection in the first region and a second interconnection in thesecond region, wherein the second interconnections includes a firstportion adjacent to the air gap, wherein a top surface of the portion islower than a top surface of the barrier pattern, wherein the secondinterconnection has a first recess formed on an edge thereof, the edgedefined by a top surface of the first portion in contact with one of thesidewalls, wherein the first interconnection has a second recess formedon an edge thereof, the edge defined by a top surface of the firstinterconnection in contact with one of the sidewalls, wherein a bottomend of the first recess is lower than a bottom end of the second recess.12. The semiconductor device of claim 11, wherein the interlayerinsulating layer includes a insulating layer and a second insulatinglayer that are sequentially formed, wherein the second insulating layercovers top surfaces of the interconnections and surrounds the air gap,and wherein a top surface of the first insulating layer of the firstregion is lower than a top surface of at least one of theinterconnections in the first region.
 13. The semiconductor device ofclaim 11, wherein a top surface of the interlayer insulating layer ofthe first region is coplanar with a top surface of the interlayerinsulating layer of the second region.
 14. The semiconductor device ofclaim 11, wherein the second interconnections further includes a secondportion in a central region thereof, and wherein a top surface of thesecond portion is higher than a top surface of the first portion.
 15. Asemiconductor device comprising: an interlayer insulating layer on asubstrate; a plurality of interconnections in the interlayer insulatinglayer; and a plurality of barrier patterns between the interlayerinsulating layer and the interconnections, respectively, wherein each ofthe barrier patterns covers a bottom surface and both sidewalls of eachof the interconnections, wherein the interlayer insulating layerincludes an air gap between first and second interconnections of theinterconnections, wherein the first interconnection has a first recessformed on a first edge thereof and a second recess formed on a secondedge thereof opposite to the first edge, wherein the first edge isdefined by a top surface of the first interconnection in contact withone of the sidewalls, wherein the second edge is defined by the topsurface of the first interconnection in contact with an opposing one ofthe sidewalls, wherein a bottom end of the first recess is lower than abottom end of the second recess.